When drawing One Piece, Eiichiro Oda was heavily influenced by the manga Dragon Ball, and had the series in mind when designing his characters. Oda has said that when he was creating Luffy, he was thinking about "manliness", because Dragon Ball had already done all the things that a child could possibly be happy about.
Luffy was first featured as the main protagonist in the first pilot of One PieceRomance Dawn V.1 in the Shonen Jump specials showcasting upcoming artists, about a year and a half before One Piece began. He would remain as the main protagonist in the second release of Romance Dawn, Romance Dawn V.2 (featured in Weekly Shonen Jump magazine itself) and the final version Romance Dawn V.3.
Luffy's character changed throughout all three versions of Romance Dawn. Starting from Romance Dawn version 1, Luffy was much smarter than his final incarnation and while he had the power of the Devil Fruit he did not seem to have any named attacks. He claimed to be a candidate for pirate and a Peace Maine type of pirate. His background story was near enough identical to the final story released with Romance Dawn version 3, with a number of noteworthy differences. The major difference being that Higuma was absent from the story in this version. Another minor difference was that Shanks' arm was bitten off by a shark instead of a Sea King. In Romance Dawn V.1 there was also a panel that featured a Luffy as captain of his own crew. This is the only time an older version of Luffy has been drawn by Oda in regard to the One Piece storyline.
Version 2 of Romance Dawn featured a Luffy closer to the final version than Romance Dawn version 1. He now had a named attack (though it featured a different naming scheme to the final version) and lacked the intelligence he displayed in Romance Dawn version 1, however, it is arguable that he was less intelligent than his final design overall. His story, though still featured him eating the Devil Fruit, did not feature Shanks and instead Luffy got both his hat and the Devil Fruit he ate from his grandfather. Luffy remained a Peace Maine type of pirate in this version and was still promoting himself as a candidate for a pirate while seeking to join up with a crew.
In both versions, Luffy was missing the scar under his left eye and he had a slightly different jolly roger. Apart from this the only difference in Luffy's overall appearance was the adaptation to suit the drawing style of each Romance Dawn. The most note worthy change from each version was of Young Luffy, whose head and body shape, though remained roughly the same, was different enough to notice.
In the anime, Luffy's past did not include the scene where he stabbed himself under the eye to prove to Shanks that he was a man, and most likely got it from Higuma. Although in the One Piece: Episode of Luffy Special the scene of him stabbing himself under his eye does appear. The anime also skipped over all the scenes before Shanks gave Luffy juice, these scenes showed Shanks making fun of Luffy for being a child as well as some of the interaction between Shanks, Luffy and the rest of Shanks' crew.
In the manga, post-timeskip Luffy is capable of using Gear Second maintaining it in a single part of his body, while in the anime, he shows no such difference, requiring his entire body once more to turn red and emit steam like previously.
Luffy appeared in a Shonen Jump special, where Enel attacks Tokyo and Odaiba. Goku arrives to fight Enel and Luffy appears to help him. Luffy and Goku make an attack called "Gomu Gomu no Kamehame Ha" and they destroy Enel.
Luffy and other characters also appeared in "Cross Epoch" with Dragon Ball characters. In this story, after Luffy falls from a cliff, Goku orders the Kinto'un to save Luffy from the fall, and then, he rides the Kinto'un until they arrive in the tea party. Being able to ride the Kinto'un, in the universe of Dragon Ball, means that Luffy is pure of heart.
In Episode 56 of Yakitate!! Japan, there is a parody of One Piece where Kuroyanagi turns into a "Tenobi Man" as a reaction from trying Azuma's Japanese-Style Ja-pan dumpling. To this effect, he dons a straw hat and starts stretching his arms like rubber to unbelievable lengths like Monkey D. Luffy.
In a fake movie preview during an episode of Gintama, Isao Kondo (playing a lookalike of Crocodile) is seen charging towards heroine Tae Shimura. Tae defeats him with a "Gomu Gomu" move. Similar enemies and attacks are also performed connected to Dragon Ball and Bleach in the same film.
In Episode 128 of Inuyasha, while at the school, a kid dressed like Monkey D. Luffy makes a minor appearance.
In Episode 2 of the anime Hayate the Combat Butler, when the "very generous people" are planning to deport him by boat, Hayate goes though a scenario in his head where he is kidnapped by pirates, joins them and dying at the hands of sea monkeys. He ends it with "Thus ends my dream of being king of the pirates" while wearing Luffy's trademark hat.
In an episode of Sayonara Zetsubou Sensei, in Harumi's room, action figures of Luffy, Zoro, Sanji and Sogeking are visible.
In the chapter 139 of the manga Rookies, a girl is shown having a Luffy doll cell phone strap.
In Episode 7 of the anime Macademi Wasshoi!, Suzuho uses the attack Gomu Gomu no Pistol.
In Gintama Volume 4, page 70, 2nd panel, Gintoki is seen reading a copy of Shonen Jump with Luffy on the cover.
In Episode 3 of the anime Highschool of the Dead, a zombie bearing a resemblance to Luffy and wearing his Straw Hat is seen walking outside a convenience store but is hit by the bus the main characters are driving.
Bakuman is a story of two students who want to become mangakas and publish their works in Shonen Jump (named Shonen Jack in the anime). It frequently makes references to or features One Piece as well as various other Shonen Jump mangas in its artwork and storyline.
In the MMORPG, Gaia Online, there is an item called "King of Fruits" that is based on One Piece and contains Luffy's signature straw hat as a pose.
In Episode 9 of Asobi ni Iku yo!, Muttley is seeing an anime that mentions a man of rubber - possibly Monkey D. Luffy.
In Chapter 90 of Bobobo-bo Bo-bobo, Bo-bobo uses a move against Torpedo Girl called "Nosehair Bazooka", an obvious parody of Monkey D. Luffy's' attack, Gomu Gomu no Bazooka.
In a chapter cover of D.Gray-Man, there is a volume of One Piece with Luffy on the cover laying on the floor.
In Episode 13 of Gintama, Gintoki and Katsura disguise as pirates to get into an alien ship. They said they were searching for the treasure "One Park", an obvious play-on-words of "One Piece".
In the manga of Rosario + Vampire Volume 3, page 22 where they say "Let us out, let us out here" Monkey D. Luffy makes a cameo appearance.
In Chapter 339 of Gantz, some people in a cage are singing "We Are!".
In Episode 20 of Fairy Tail when Happy hatches from an egg, a crowd of people gather around him, and one of these characters is shown wearing Luffy's pre-timeskip attire. Also in episode 205, Luffy made a cameo appearence in the first scene.
In Chapter 16 of Dreamland, there is a character who looks like Luffy saying "Food Time".
In an episode of Gintama, Gintoki reads fan mail in which one fan asks what the goal of Gintama is yet Gintoki himself doesn't know. So they have decided (as a joke) the goal would be Gintoki becoming the king of the samurai referencing Luffy's journey to be king of the pirates. Also Gintoki is shown in a picture wearing Luffy's former attire also while being on the Thousand Sunny with the Lion head replaced with Elizabeth's.
In an episode of Highschool DxD, Issei Hyoudou says that he wants to become the "harem king" in a manner extremely similar to Luffy.
In Beelzebub, the director of Ishiyama Academy has got a straw hat that makes reference to Monkey D. Luffy
Monkey D. Luffy makes cameo appearence in the episode 18, 2nd season of Wakfu.
In Naruto manga chapter 700 on Naruto's face on the Hokage Monument, Boruto paints the Straw Hat Pirates' jolly roger.
Also, in the Naruto manga spin-off, Boruto: Road to B, when Boruto's teammate Mitsuki shows his ability to stretch his limbs, Boruto asked him if his father is Monkey. D. Luffy, which Mitsuki quickly denied.
In episode 3 from Sora no Otoshimono Forte, Tomoki use mano mano no handling, a reference to Gomu Gomu no Gatling.
In the fighting video game, The King of Fighters XIII, the move of Ralf's Jet Vulcan Punch is based on Gomu Gomu Jet Gatling.
In the manga: Hetalia World Stars, Chapter 11, North Italy cosplayed as Luffy in expensive clothing, and sent Germany a text saying that he was going to be the Pirate King.
Yuzuki Fuwa is imitating Luffy's Gear Second iconic posture in the chapter 162 of Assassination Classroom. In Season 2, Episode 21 of the series, Korosensei puts his students in a giant bag and uses "Gum-Gum Slingshot" to send them flying, during which he holds onto a goal post and stretches like a slingshot to carry out the action.
Though some translations dub his name as "Ruffy" or "Rufi", Oda himself made it clear that "Luffy" was the correct spelling of the name.
Oda has claimed that at the time of naming Luffy, he did so because he felt the name "Luffy" was right for his main character. Later Oda found out there is a Maritime term called a "Luff" and has insisted this is pure coincidence but one he was delighted by. Up until this point, this had previously been noted by fans and some considered it intentional.
In the Viz English manga, 4Kids and FUNimation dubs, the most common alteration seen to Luffy is the reference to his Devil Fruit, the Gomu Gomu no Mi, as the "Gum-Gum Fruit." The correct term would be the "Rubber Rubber Fruit," which has not been used outside the Odex version of the series (For example, Gomu Gomu no Fusen is translated as "Rubber Balloon"). This is, however, often considered an unfortunate necessity, as fitting "Rubber-Rubber" into the allotted animation "lip-flap" and time is nearly impossible without sounding rushed or otherwise ridiculous; "Gum-Gum," naturally, fits perfectly.
Other alterations in the 4Kids dub are mainly directed around the renaming of most of his attacks, most away from references to guns (such as the Gomu Gomu no Pistol, which becomes Gum-Gum Blast), but not traditional weapons (Gomu Gomu no Ono/Gum-Gum Axe). Other than attacks, Luffy is constantly the center of attention for the removal of blood in battles against foes. All of these are common censorship edits made for American TV. With the recent changeover of the dubbing company, FUNimation took a more relaxed approach to editing, and retained the firearm references, as well as a gratuitous level of blood shown. By Episode 177, the anime appears to be fully uncut.
In the book The Anime Encyclopedia: A guide to Japanese animation since 1917 (2001), there was a short article about One Piece. In it there were 3 mistakes concerning Luffy; his age was written as 16, his name was spelled Rufy and he was written to have saved Shanks' life instead of the other way round.
Luffy's blood-type is type F, the same as Reiju's, Jinbe's and Vivi's.
Luffy's participant number at the Corrida Colosseum (as Lucy) is 0556. That number can be explained with the first two digits taken from Luffy's birthday, May 05; and the latter two, 5-6, being pronounced go-mu which is related to Luffy's Devil Fruit.
Luffy's participant number at the Corrida Colosseum also corresponds to the chapter where he first arrived at Marineford to rescue his brother, Portgas D. Ace from his execution.
Luffy often recalls his crew members in the order of them joining the crew: "Zoro, Nami, Usopp, Sanji, Chopper, Robin, Franky and Brook."
Luffy ranks first place in every popularity poll.
Luffy is very similar to Son Goku from Dragon Ball, being the main character, being very childish and naive, having messy black hair and eating too much food. These similarities are fitting since Oda was inspired by Dragon Ball while creating One Piece.